Sediment geochemistry and tectonic setting: Application of discrimination diagrams to early stages of intracontinental rift evolution,with examples from the Okavango and Southern Tanganyika rift basins |
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| Authors: | P Huntsman-Mapila J-J Tiercelin M Benoit S Ringrose S Diskin J Cotten C Hémond |
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| Institution: | 1. TU Bergakademie Freiberg, Geological Institute, Department Palaeontology/Stratigraphy, Bernhard-von-Cotta-Str. 2, 09599 Freiberg, Germany;2. Kazan Federal University, Kremlyovskaya str. 18, 420008 Kazan, Russia;3. Geology Department and Albany Museum, Rhodes University, Grahamstown 6140, South Africa;1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China;2. Department of Geological Sciences, Indiana University, Bloomington, IN 47405, USA;3. ISTerre, Université Joseph Fourier, 38400 St Martin d''Hères, France;4. School of Earth Sciences and Key Laboratory of Mineral Resources in Western China Guansu Province, Lanzhou University, Lanzhou 730000, China;1. Instituto de Energías Renovables, Universidad Nacional Autónoma de México, Av. Xochicalco s/no., Col. Centro, Temixco, Mor. 62580, Mexico;2. Instituto de Ciencias del Mar y Limnología, Procesos Oceánicos y Costeros, Universidad Nacional Autónoma de México, Circuito Exterior s/n, 04510, México D.F., Mexico |
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| Abstract: | In this article, we have applied discriminant diagrams and bivariate plots for tectonic setting to Quaternary sediments from the East African Rift System (EARS). Sediment samples used in this study represent two different phases in early stage intracontinental rift evolution: the alluvial fan of the nascent Okavango system and a lacustrine basin within the relatively more mature Tanganyika system. The diagrams for tectonic setting for major elements place the majority of these EARS sediments within the passive margin (PM) setting. Passive margin sandstones are generally enriched in SiO2 and depleted in Na2O, CaO and TiO2 reflecting their highly recycled nature. Based on major element discriminant diagrams, we propose two new fields for early stage intracontinental rift evolution (alluvial fan and lacustrine basin), within the previously defined passive margin field. The rare earth element (REE) patterns from both Okavango and Tanganyika sediments exhibit patterns similar to PAAS, with ash layers from the Rungwe volcanics in the Tanganyika samples exhibiting an enrichment in REE relative to the bulk sediment. |
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